Abstract: Purity control in producing metallic strontium using vacuum aluminothermic reduction was analysed by thermodynamic calculation.The differentiae of the critical reduction temperature and vapor pressure of Sr,Ba and Ca were discussed,and the purity of metallic strontium was controled.The results showed that BaO was the most unstable one to be reduced easily,CaO was the most stable one to be reduced dificultly,and SrO was in between.The vapor pressure of Sr increased with higher temperature,resulting in easy distillation of Sr;At 1 273 K,the vapor pressure ratio of Sr to Ca was about 2.4,making Ca difficult to be distilled,while the ratio of Sr to Ba was about 28.5 making Ba easy to be distilled.High purity metallic strontium with w(Sr)≥99.5%,w(Ba)<0.20%,w(Ca)<0.05% can be produced using excellent-grade industrial pure strontium carbonate and pure aluminum Al99.80 under following optimized conditions,(1 050±20) ℃,0.01 kPa,15 h.